Random address electro-optical switch



Oct. 14, 1969 G. R. SPENCER ET AL RANDOM ADDRESS ELECTRO-OPTICAL SWITCH Filed Feb. 1, 1967 Unted States Patent O ABSTRACT F THE DISCLOSURE A random address electro-optical switch comprising an array of light-emitting diodes that may be modulated over the frequency spectrum of the input signal. Each of the light emitters is driven from its corresponding signal source by an amplifier positioned between the signal` source and the light emitter. The light emitted by each diode of the array is imaged onto the photocathode surface of an image-dissector type of image tube. A simple lens system is .employed to image the light emitted `onto the photocathode. An electron-collecting aperture that is scanned by an electron image from the photocathode selects a single light-emitting element or an area of the light-emitting array. Positioning of the image is accomplished by a deliection coil surrounding the envelope of the tube. An electron multiplier multiplies the portion of the electron image intercepted by the aperture. The electrical signal output of the electron multiplier is proportional to the light falling on that portion of the image dissector photocathode corresponding to that portion of the electron image intercepted by the aperture.

BACKGROUND OF THE INVENTION A problem exists in a phased array antenna which produces n simultaneous beam outputs, which cover the entire field of View of the antenna. The problem is how to select a single beam output from all the beam outputs. The selection must be readily time switchable in order to be compatible with the methods of operation of a phased array.

An object of the present invention is to provide a r'andom address electro-optical switch which may be utilized in selecting a single output from among a large number of inputs.

Another object of the invention is to provide a random address electro-optical switch which may be utilized in selecting a single output beam from among a large number of input beams in a phased array antenna.

A further object of the present invention is to provide a random address electro-optical switch which may select the output of a single light-emitting element or the output of a small area from a light-emitting array from a large number of lightemitting elements or large array.

A further object of the present invention is to provide a random address electro-optical switch which facilitates the programming of the selection of antenna elements in a desired time sequence in order to achieve antenna beam steering.

The present invention can be implemented to solve the switching problem associated with a phased array antenna or in any other situation where it is desirable to select a single signal output from among a large number of signal inputs. The approach of the present invention oiers a number of advantages over other approaches to the same problem, such as from diode switches, which are as follows: (l) Ready random access to any point on a large matrix; (2) high signal-to-noise ratio; (3) very low crosstalk; (4) overall system simplicity; (5) capability for switching high IF frequency; and (6r) wide signal bandwidth.

3,473,076 Patented Oct. 14, 1969 'ice SUMMARY OF THE INVENTION The above objects and advantages of the present invention are accomplished by providing a random address electro optical switch for selecting a single output signal from among a large number of input signals, the switch comprising: an array of light-emitting means which may be modulated over the frequency spectrum of the input signals; means for driving each of the lightemitting means from the corresponding electrical signal inputs, each of the driving means being connected to a source of input signals; image-dissecting means positioned adjacent but separated from the light-emitting means; means positioned between the light-emitting means and the image-dissecting means for imaging the output from the light-emitting means into the image-dissecting means; means for selecting and positioning a signal from an area of the light-emitting means; and means for amplifying the selected signal, the selected signal output being proportional to the light faling on the area of the image-dissecting means which corresponds to the area selected by said selecting means.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic view of the light-emitting elements of the present invention;

FIG. 2 is a schematic diagram of one embodiment of the present invention; and

FIG. 3 is a schematic diagram of an alternative embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Like reference characters are used throughout the several views to designate like or similar elements.

FIG. l shows an array 10 consisting of rows and columns of light-emitting diodes 12. The diodes 12 may be modulated over the frequency spectrum of the input signals which are applied thereto. Although the light-emitting elements are described as diodes 12, any other lightemitting source which may be modulated over the Irequency spectrum of the input signals may be utilized. Further, although the diodes 12 are arranged in rows and columns, any other coniiguration may be employed which is suitable to the problem being solved. Basically, the diodes 12 are arranged on a surface in a geometrical order which corresponds to the arrangement of the beams of the array in space.

FIG. 2 shows a random address electro-optical switch 20 of the present invention. The light-emitting sources are diodes 12, arranged in rows and columns as shown in FIG. l. Each of the light emitters 12 is driven from a corresponding input signal source shown at terminals 22. These signal sources may be provided by the individual antenna elements of a phased array. Connected between each of the input signal sources at terminals 22 and the light emitters 12 is an amplifier 24 which amplifes the signal suiiiciently to drive each of the light emitters 12. Although each diode 12 is shown as being driven by an amplifier 24, in some cases the input signals may be sufcient so that a driving amplilier is unnecessary. The light emitted -by each light emitter 12 is imaged onto a photocathode surface 26 of an image vdissector tube 28 having a transparent faceplate 25 made of a material such as glass. A simple lens system represented by the lens 30, which is positioned betwen the light emitters 12 and the image-dissector tube 28, images the light emitted by each of the light emitters 12 onto the photocathode surface 26. The photocathode surface 26 has a potential -V applied thereto via a terminal 27.

Upon striking the photocathode surface 26, the light p 3 ward an anode surface 34. The anode surface 34 has a potential -i-V applied thereto via a terminal 29. A focus coil 36 surrounds the tube 28 and causes the photo electrons 32 emitted from each point on the photocathode to converge to a corresponding point in the plane defined by' the anode surface 34, forming an electron image.

The output from a single light emitter 12 or from an area of the light-emitting array may be selected for amplification and further processing by the image-dissector tube 28. The selection is accomplished by deflecting the electrons 32 by means of a deflection coil 40 so that the electron image is positioned laterally in the `anode surface 34 to make that portion of the image corresponding to the desired light emitter coincide with an electroncollecting aperture 38. The deflection coil 40 is driven via appropriate X and Y amplifiers from X 'and Y selection signals (not shown). The deflection coil 4l) positions the electron image corresponding to the desired light emitter 12 into the electron-collecting aperture 38. The aperture 38 is parallel to and lies in the plane of the anode surface 34 which forms the electron focus plane. The area of the electron image that forms the output signal from the image-dissector tube 28 is the area intercepted `by the aperture 38.

Positioned at the end of the tube 28 opposite the photocathode surface 26 is an electron multiplier 42 which is contained within the vacuum envelope of tube 28, and which extends to the same vertical plane defined by anode surface 34 in which the aperture 38 lies. When the Selected single beam output strikes the aperture 38 it passes into the multiplier 42. The electron multiplier 42 comprises an array of secondary emitting dynodes 46 connected to sources of successively higher positive voltages V2, V3, V4, V5, etc., and having surfaces of secondary electron emission ratios greater than unity. The electron current entering the aperture 38 is multiplied in the multipliei 42 `by the factor (-l)n, where is the secondary emission ratio and n the number of dynodes. The electron multiplier -42 is terminated in an output eletrode 49 from which the output signal is extracted on an electrical feedthrough line 48.

The signal output of the electron multiplier 42 is terminated in a load RL 47 which is connected between the feedthrough line 48 and ground. The load RL 47 is provided to translate the output signal from the multiplier 42 from a current signal to a voltage signal. The electrical signal out of the electron multiplier 42 is proportional to the light falling on that portion of the photocathode surface 26 of the image-dissector tube 28 corresponding to the portion of the electron image intercepted by the aperture 38.

FIG. 3 shows an alternative embodiment of the switch 20 of FIG. 2. In place of the lens 30 a plurality of fiber optic light pipes 50 is provided each of which conducts the output from a light emitter 12 to the photocathode surface 26 of image-dissector tube 28. Although the fiber optic light pipes 50 are shown as being straight, they may be flexible so that the light may travel in other than a straight line path. Also, the tube 28 instead of having a regular transparent faceplate, such as plate 25, has a fiber optic faceplate 52. However, in all other respects, the embodiment shown in FIG. 3 is structurally and functionally the same as the embodiment in FIG. 2.

The following set of typical system parameters may be employed with the present invention. An array of 1600 elements, a l0 mHz. bandwidth and a convenient IF frequency, such as 30 mHz., may be employed. The light emitters 12 may be galliurn arsenide diodes. A Fresnel lens, which approximates the theoretical maximum aperture f/ 0.5, may be utilized since lens aberrations are not a problem. In achieving the desired result, it is necessary to capture a 20 included angle cone of light from the diode, which is based on the published radiation pattern for the diode used, in order to give the maximum allow- Iable average current density over the illuminated portion 4 of the photocathode surface. Assuming that the diode is percent modulated with the signal, the maximum signal-to-noise ratio at the output of the image dissector tube can be determined by:

where IS=image dissector RMS output signal current In=image dissector RMS output noise current I=RMS light at the photocathode per channel, w L=average light at the photocathode per channel, w S=sensitivity of photocathode, a/w

:gain of multiplier F=noise contribution from multiplier, typically 1.25 Id=dark current Bzbandwidth, c.p.s. e=electronic charge, 1.6 10'19 coulombs A signal-to-noise ratio for 100 percent diode modulation of 33 db may be obtained. The diode light power is directly proportional to diode current so that the diode must be driven by a current source. It should be noted that it would be possible to sum the outputs from several of the light-emitting elements in the array by properly choosing the size and shape of the image dissector scanning aperture.

The maximum number of beams one might wish to handle per tube is probably limited more by the problern of scanning precision and repeatability rather than by resolution. Linearity is not an important requirement and a moderate amount of distortion, due either to scanning or to the optics, is permissible as long as it is constant. If it is desired to handle antennas having a larger number of beams than a single tube can handle, it is simple enough to split the antenna up among a number of switching tubes.

Tubes of this sort can be built with more than one aperture/electron-multiplier at the output. If this is done, true simultaneous monopulse or other forms of 'beam clustering are then readily obtainable by having each tube look at four adjacent beams.

The flexibility of this optical approach also makes it possible to have true monopulse using four separate tubes. This can be done by mapping the antenna outputs so that four spatially adjacent beams are always found to fall on four separate tubes. 'Ihe following sketch of a section of the radars field of view (in two angular coordinates) shows this:

will always contain all four numbers. The four outputs can be connected` in parallel to form a sum channel; the 2-4, and the 1-3 combinations can be diierentially connected to form X and Y error signals. The sense and direction of each error output depends on the group 5 being examined.

Although the present invention has been described in conjunction with selecting a single output beam from a phased array antenna, it is not limited to this application. The random address electro optical switch of the present invention may be employed wherever it may be desirable to select a single output from among a large number of inputs. Obviously, many modifications and variations of the present invention are possiblein the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

We claim:

1. A random address electro-optical switch for selecting a single output signal from among a large number of input signals, said switch comprising:

an array of light-emitting means which may be modulated over the frequency spectrum of the input signals;

means for driving each of said light-emitting means from the corresponding signal input, each of said driving means being connected to a source of electrical input signals;

image-dissecting means positioned adjacent but separated from said light-emitting means;

means positioned between said light-emitting means and said image-dissecting means for imaging the output from the light-emitting means into said imagedissecting means;

means associated with said image-dissecting means for selecting and positioning a single output signal from an area of said light-emitting means at a particular location within said image-dissecting means; and means for amplifying the selected signal, said selected signal output being an electrical signal which is proportional to thelight falling on the area of the image-dissecting means which corresponds to the area selected by said selecting means.

2. A random address electro-optical switch as set forth in claim 1 wherein:

said array of light-emitting means is an array of lightemitting diodes arranged in rows and colums.

3. A random address electro-optical switch as set forth in claim 1 wherein:

said means for driving each of said light-emitting means is an amplier.

4. A random address electro-optical switch as set forth in claim 1 wherein:

said image-dissecting means includes an image-dissector tube having a photocathode surface upon which the light emitted is imaged.

S. A random address electro-optical switchas set forth in claim 1 wherein:

said means for imaging the output from the lightemitting means into said image-dissecting means includes a simple lens system.

6. A random address electro-optical switch as set forth in claim 1 wherein:

said means for imaging the output from said lightemitting means into said image-dissecting means includes a liber optic light pipe associated with each light-emitting means of said array.

7. A random address electro-optical switch as set forth in claim 1 wherein:

said -selecting and positioning means includes an image dissector tube with a photocathode surface and having an electron-collecting aperture which is scanned by an electron image from the photocathode surface and a detlection coil surrounding said tube.

8. A random address electro-optical switch as set forth in claim 1 wherein:

said amplifying means includes an electron multiplier.

9. A random address electro-optical switch for selecting a single output signal from among a large number of input signals, said switch comprising:

an array of light-emitting diodes arranged in rows and columns which may be modulated over the frequency spectrum of the input signals;

a plurality of ampliers each being connected to one of said diodes for driving each of said diodes from the corresponding signal input, each of said amplifiers being connected to a source of input signals;

image dissecting means positioned adjacent but separated from said light-emitting diodes;

means positioned between said light-emitting diodes and said image-dissecting means for imaging the output from the light-emitting diodes into Isaid imagedissecting means;

means for selecting and positioning a signal from an larea of said light-emitting diodes; and

-means for multiplying the selected signal, said selected signal output being proportional to the light falling on the area of the image-dissecting means which corresponds to the area selected by said selecting means.

10. A random address electro-optical switch for selecting a single output signal from among a large number of input signals, said switch comprising:

an array of light-emitting means which may be modulated over the frequency spectrum of the input signals;

means for driving each of said light-emitting means from the corresponding signal input, each of said driving means being connected to a source of input signals;

an image-dissecting tube positioned adjacent but separated from said light-emitting means, sai-d tube having a photocathode surface upon which the light emitted is imaged;

a lens positioned between said light-emitting means and said image dissecting tube for imaging lthe output from the light-emitting means on the photocathode surface of said tube;

means for selecting and positioning a signal from an area of said light-emitting means; and

means for multiplying the selected signal, said selected signal output being proportional to the light falling on the area of the image-dissecting tube which corresponds to the area selected by said selecting means.

11. A random address electro-optical switch for selecting a single output signal from among a large number of input signals, said switch comprising:

an array of light-emitting means which may be modulated over the frequency spectrum of the input signals;

means for driving each of said light-emitting means from the corresponding signal input, each of said driving means being connected to a source of input signals;

image-dissecting means positioned adjacent but separated from said light-emitting means;

means positioned between said light-emitting means and said image-dissecting means for imaging the output from the light-emitting means into said imagedissecting means;

said image-dissecting means including an image dissector tube having a photocathode surface at an end nearest said light-emitting means upon which the light emitted is imaged and an electron-collecting aperture at the end opposite said photocathode surface;

a deection coil surrounding said tube for selecting and positioning the output from a single light-emitting means into said electron-collecting aperture; and

an electron multiplier into which the electron image intercepted by said aperture is directed, the multiplier signal output being proportional to the light falling on the photocathode surface which corresponds to the single light-emitting output selected and positioned in said electron-collecting aperture by said dellection coil.

12. A random address electro-optical switch for selecting a single output signal from among a large number of input signals, said switch comprising:

an array of light-emitting diodes arranged in rows and column-s which may be modulated over the frequency spectrum of the input signals;

means for driving each of said light-emitting diodes from the corresponding signal input, each of said driving means being connected to a source of input signals;

an image-dissecting tube positioned adjacent but Separated from said light-emitting means, :said tube having a photocathode surface upon which the light emitted is imaged;

means positioned between said light-emitting diodes and said image-dissecting means for imaging the output from the light-emitting diodes into said image-dis- :secting tube;

said image-dissecting tube having an electron-collecting aperture at the end of `said tube opposite said photocathode surface;

a deflection coil surrounding said tube for selecting and positioning the output from a single light-emitting diode into said electron-collecting aperture; and

means for multiplying the selected signal, said selected signal output being proportional to the light falling on the photocathode surface of the image-dissecting tube which corresponds to the single light-emitting output selected and positioned in said electron-collecting aperture by said deection coil.

13. A random address electro optical switch for selecting a single output beam from among a large number of input beams of a phased array antenna, said switch comprising:

an array of light-emitting diodes arranged in rows and columns which may be modulated over the frequency spectrum of the input beams;

a plurality of amplifiers each being connected to one of said diodes for driving each of said diodes from the corresponding input beam, each of said amplifiers being connected to a source of an input beam;

an image-dissecting tube positioned adjacent but separated from said light-emitting diodes, said tube having a photocathode surface at one end thereof upon which the light emitted is imaged;

a lens positioned between said light-emitting diodes and :said image dissecting tube for imaging the output from the light-emitting diodes on the photocathode surface of said tube;

said image-dissecting tube having an electron-collecting aperture at the end of said tube opposite said photocathode surface;

a focus coil surrounding said tube for focussing the electrons striking said photocathode surface into an electron focus plane, said aperture being located in the same vertical plane as that of the electron focus plane;

a deflection coil surrounding said tube for selecting and positioning the output from a single light-emitting diode into said electron-collecting aperture; and

an electron multiplier into which the electron image intercepted by said aperture is directed, the multiplier lsignal output being proportional to the light falling on the photocathode surface which corresponds to the single light-emitting output selected and positioned in said electron-collecting aperture by :said deection coil.

References Cited UNITED STATES PATENTS 3,305,673 2/1967 Bray Z50-209 X 3,322,955 5/ 1967 Desuignes 250--209 3,388,255 6/1968 May Z50-217 XR 3,399,305 8/1968 Sibley 250-209 RODNEY D. BENNETT, JR., Primary Examiner 40 JEFFREY P. MORRIS, Assistant Examiner U.S. Cl. X.R. 

